Field testing in Assam Field testing for Fluoride, Arsenic and Total Iron at Nalbari, Assam. Image courtesy, Ishan Gupta

ffem test devices are open source. They are designed for field use. Typically, ffem tests cost much less than a laboratory test, while they are a lot more precise than a field test kit.

ffem Water

A water testing kit with drinking water, and lake and river water monitoring parameters.

Complete listing of water quality test kits and parameters.

ffem Soil

Soil test kit for soil macronutrients NPK and pH.

Complete listing of soil test kits and parameters.

Working principle

Current test devices are based on colorimetry. The kits use the camera and flash of a smartphone to detect a colour change created by certain specific reagents. The colour change is compared to a series of calibrated colours and a suitably interpolated result is displayed.

The test method for Fluoride was published in a peer reviewed journal Link PDF. All other tests work on the same principle.


The product may sometimes be referred to as Caddisfly, ffem Caddisfly, ffem Water or ffem soil.